Pyridine hydrogenation and piperidine hydrogenolysis on a commercial hydrocracking catalyst I. Reaction and deactivation kinetics

Abstract

The vapor phase kinetics of pyridine hydrogenation over a commercial fresh hydrocracking catalyst were studied in a continuous-flow fixed-bed reactor and the feasibility of this reaction as a probe for characterizing the catalyst was examined. Kinetic experiments at total pressures of 13.01 to 13.48 atm, temperatures of 312 to 334°C, and initial pyridine partial pressures of 0.116 to 0.483 atm indicated that pyridine hydrogenation to piperidine was the predominant reaction and that the reaction rate was first order in pyridine. The feasibility of piperidine hydrogenolysis as a probe for characterizing dual-functional catalysts was also examined and the reaction and deactivation kinetics of this system were studied in the above reactor operating at integral conversions. The kinetic studies were conducted at total pressures of 15.86 to 16.14 atm, temperatures ranging from 281 to 321°C, and initial concentrations of piperidine from 4.03 to 11.84 × 10 −3 mol/liter. Product distributions revealed that the predominant reactions were only those converting piperidine to other nitrogen-containing compounds. Both the metallic and acidic catalyst functions were active simultaneously in the conversion reactions and both were deactivated under conditions of the experiments. To offset catalyst deactivation effects, the conversion data were extrapolated to zero time on stream. The kinetic parameters were determined using a reaction-deactivation model based on separable kinetics. The reaction rate data were best fit to Langmuir-Hinshelwood type expressions proposing two different catalytic sites for hydrogen and nitrogen compound adsorption.